The present invention relates to improvements in flexible containers, in particular, to a method and apparatus for making an improved zipper base with grip strip, and to the improved, easy-open, reclosable flexible container structure produced thereby.
Flexible containers made of thermoplastic film and having reclosable interlocking zipper elements are well-known and widely used. Where such containers are hermetically sealed across the bag mouth, various easy-open features have been devised to first break the seal before accessing the bag contents. Once opened, interlocked zipper elements may be opened by grasping the opposing bag lips and pulling them apart. Thus, various means for gripping have also been devised to improve the user's grip on the surfaces of opposing bag lips.
Among the easy-open features in the prior art are perforated or weakened lines of tearing. Boeckmann et al, U.S. Pat. No. 4,846,585, and Van Erden et al, U.S. Pat. No. 4,589,145, show such lines of tearing and provide seal strips along the lines of tearing to maintain the hermetic nature of the sealed container.
Various means for gripping are shown, for example, by Scheibner, U.S. Pat. No. 4,363,345, who discloses a grip strip comprised of one or two ribs extruded onto the inner surfaces of bag lips. In European Pat. No. 0089680, Scheibner further discloses patterns embossed or engraved on the bag lip surfaces to provide non-slip surfaces, and the use of anti-slip materials, such as particulates, added to the plastic in the area of the bag lips to enhance gripping. See also, McCree, U.S. Pat. No. 5,009,828; issued 4-23-91, based on Ser. No. 419,975, filed Oct. 11, 1989.
Some easy-open features have been designed to also serve as a means for gripping. For example, Uramoto, in U.S. Pat. Nos. 3,827,472 (the '472 patent) and 3,780,781 (the '781 patent), discloses sealed, easy-open flexible containers which include means for tearing, parts of which remain in the bag mouth after opening to serve as means for gripping the bag lips. More specifically, in the '472 patent, sealed flexible containers, made from a film laminate having an inner and outer layer, include ribs on the inner layer either side of a tear line made in the inner layer. When the flexible containers are opened along the tear line, a single rib remains on the inside layer of each bag lip to assist in gripping the bag lips.
In the '781 patent to Uramoto and the embodiment of FIG. 13 thereof, a thermoplastic reinforcing strip is laminated to the inside surface of a container. The reinforcing strip extends across the top edge of the container and serves as a base for both zipper elements. The reinforcing strip includes opposing perforated or weakened tear lines, with ribs laminated, extruded onto, or adhered on either side of each tear line. As in the '472 patent, once the container is opened, a single rib remains on the inside layer of each bag lip to serve as a grip strip.
Among the problems encountered in producing flexible containers with easy-open features, grip strips, and reclosable zipper elements, is the concentration of the various dies needed to produce desired elements and features on the film. The area in which the various features are to be applied to the film is narrow, and space limitations make difficult the installation, adjustment and maintenance of the dies, as well as other adjacent equipment. For example, in accordance with prior art methods, eight dies are needed to produce thermoplastic film with interlocking zipper elements; bases such as shown by Kamp, U.S. Pat. No. 4,428,788; opposing areas of grip strips or ribs; and first and second seal strips for first and second perforated lines of tearing. That is, two dies are required for the zipper elements, two for the bases on which the zipper elements mount to the film, two for the opposing areas of grip strips, and two for the first and second sealing strips which seal the first and second perforated lines of tearing.
Accordingly, improvements are desired to overcome continuing problems presented by the methods and apparatuses used to prepare thermoplastic film for flexible containers, particularly where such film includes various desirable features, such as zipper elements, means for tearing, and means for gripping. As well, further improvements are continually sought in the design of easy-open flexible containers.